The invention relates to a device for the contactless determination of an electrical potential of an object comprising an electrode. The invention also relates to a current probe with such a device. Finally, the invention relates to a method for the contactless determination of an electrical potential of an object.
It is known to measure the current flow through an object in contactless fashion. This can be performed via inductive coupling, the Hall effect or the GMR (giant magnetoresistance) effect. In order to be able to measure electrical power in contactless fashion, however, a method for the contactless potential measurement is also required, in addition to contactless current measurement. The contactless potential measurement, in particular of high voltages, is of particular importance primarily in the sector of smart metering, smart grid and demand response strategies.
One possibility for this is provided by so-called electric field meters. These use the effect of electrostatic induction in order to be able to draw conclusions on the voltage to be determined via the determined electric field strength. However, for this, the distance between the object whose potential is intended to be determined and the measuring electrode of the electric field meter and material (dielectric) between the measuring electrode and the object in the measurement capacitance need to be known precisely. In order to be able to measure DC voltages as well with an electric field meter, in general a shutter (field stop) in the form of a chopper (impeller) is used between the measuring electrode and the object.
In order to determine purely AC voltages, capacitive voltage dividers can also be used, wherein in this case the coupling capacitance between a reference electrode and the potential to be measured likewise needs to be known.
Both methods and devices (electric field meter and capacitive voltage divider) presuppose precise knowledge of the coupling to the voltage to be measured, in particular of the distance between the measuring electrode and the measurement object. To this extent, these known methods are unsuitable for only temporary measurement operations or retrospective measurement installations. Electric field meters and capacitive voltage dividers are installed permanently for precise measurements and calibrated in the installed environment. In the case of handheld measuring devices, precise knowledge of the geometry and material makeup (line insulation, air, gas, condensation, etc.) of the measurement setup is necessary. For this, for example, special spacers are used in conventional electric field meters. However, spacers have the disadvantage that they do not rest directly on the conductive material, in particular for the potential determination of electrically insulated lines, and therefore only insufficiently accurately set the distance. In addition, the type of insulating material cannot be taken into consideration. If this precision of the known contactless potential measurement methods is insufficient, it is generally necessary for the measurements to be taken in contact-making fashion.
EP 1 249 706 A2 describes a contactless voltage measurement method for measuring an AC voltage applied to a conductor using a detection probe comprising a detection electrode, which can cover some of a surface of insulation for insulating the conductor, and a shielding electrode for covering the detection electrode, and an oscillator for outputting a signal, wherein in each case one end of a core cable and a sheath cable of a shielded cable is connected to the detection electrode and to the shielding electrode, respectively, and wherein the influence of a potential-free capacitance is substantially eliminated by the production of an imaginary short-circuit state between the respective other ends of the core cable and the sheath cable.
WO 2008/009906 A1 describes a sensor for determining an electrical potential comprising at least one detection electrode, which is arranged for capacitive coupling to a probe in the test and for generating a measurement signal, an oscillator, which is arranged for generating an oscillator output which has a frequency corresponding to the frequency of the measurement signal, and a feedback device, which reacts to the oscillator output in order to generate a feedback reference signal in order to apply coherent feedback at the input of the sensor amplifier.
US 2006/058694 A1 discloses an electrodynamic sensor comprising a pair of input probes for detecting electrical potentials which originate from an object to be tested and for generating detection signals. In addition, the sensor comprises an electric meter, which has an amplifier and is designed to receive the detection signals and produce measurement signals.
U.S. Pat. No. 6,531,880 B1 describes a contactless cable tester comprising a sensor for detecting an electrical field, which is output by a cable. In this case, the sensor signal is compared with predetermined threshold values in order to determine the electrical energy flowing through the cable.
Furthermore, US 2007/086130 A1 describes a device for determining an AC voltage in a conductor comprising a first and a second group of capacitive voltage sensors, which are each arranged in the form of a circle around the conductor.
U.S. Pat. No. 5,473,244 A discloses a device for the contactless measurement of the voltage, the current and the power in an electrical conductor. The device comprises an arrangement comprising capacitive sensors, with which a sensor signal can be provided depending on the electrical field generated by the electrical conductor. In this case, a DC voltage can also be detected in the electrical conductor by virtue of an electrode of the capacitive sensors being moved continuously.
FR 2 924 814 A and EP 0 398 396 A2 describe systems for measuring electrical voltages. Said systems comprise capacitive sensors with which the electrical voltages in a polyphase system can be detected.
U.S. Pat. No. 4,611,207 A discloses a device for measuring an electrical voltage, which has a ring-shaped housing, which can be arranged on a high-voltage overhead line.